1. Field of the Invention
The present invention relates to a method and apparatus for forming a resist pattern, and a printed wiring board fabricated thereby. More particularly, the invention relates to a method and apparatus for forming a resist pattern necessary for circuit formation, and a printed wiring board fabricated thereby.
2. Description of Related Art
When a predetermined pattern is formed on an object, a resist is generally used. The fabrication of a printed wiring board, for example, utilizes a solder resist formation process to form a circuit pattern. This process comprises several steps each requiring a corresponding jig.
A conventional method for forming a solder resist pattern will hereinafter be described briefly with reference to FIG. 4.
A printed wiring board formed with a surface layer in a surface layer forming step 51 is subjected to six steps for the formation of a solder resist pattern on the surface of the printed wiring board, which include: a pretreatment step 52 of polishing the surface layer to improve the adhesiveness of a solder resist to the surface layer; an electrostatic coating step 53 of coating the surface layer with the solder resist; a preliminary drying step 54 of evaporating a solvent; an exposure step 55 of exposing the printed wiring board to light with a predetermined artwork mask; a development step 56 of removing an unexposed portion (in which etching may be also employed); and a heat curing step 57 of curing the solder resist. In the exposure step, a plurality of artwork masks are required for respective circuit designs.
The process for preparing an artwork mask comprises the steps of: coating a 0.2 .mu.m- to 0.3 .mu.m-thick transparent substrate such as of polyethylene with a photosensitive material of a silver salt such as silver bromide; exposing the photosensitive material to light by way of laser drawing, and developing the photosensitive material for the formation of a predetermined pattern; coating the transparent substrate with a protective film for the protection of the pattern; forming a reference hole; and inspecting the resultant artwork mask.
For Example, Japanese Patent Unexamined Patent Application No. Hei 5(1993)-338187 discloses a method for forming a resist pattern wherein an image signal for a resist pattern to be formed is sent to a ink-jet printer for printing the resist pattern on a printed wiring board. The above method, however, cannot form a uniform resist pattern on a printed wiring board which has a plurality of through holes. For the diameter of a through hole is larger than that of a ink droplet jetted by the ink-jet printer, which allows ink droplets into through holes. The through holes thus stuffed with ink droplets degrade quality of the printed wiring board.
As described above, the process for forming a solder resist pattern includes a multiplicity of steps and, hence, requires equipment and quality control consideration for each of the steps. Different artwork masks are required for different circuit designs. One printed wiring board generally includes an inner layer circuit, surface layer circuit, solder resist circuit and a like circuit, thereby requiring a plurality of artwork masks having different patterns for the formation of the respective circuits. The use of the artwork masks imposes additional requirements for quality control, cost and storage of themselves. Further, each light exposure requires placement and registration of an artwork mask on a circuit board, thus resulting in limited registration accuracy.
In the technical fields other than the printed wiring board technology, for example, the field of semiconductor devices, preliminarily patterned masks are required for the formation of predetermined patterns on a substrate, presenting the same problem as that of the aforesaid artwork masks.